When I built my wine counter in the basement, I was ramped up to construct a countertop. I had all the materials priced out at $90 USD.
I was in a home improvement store and spotted pre-built 8' long countertops ... $65 ... ok, as much as I was into building one from scratch, I put back the parts in the cart and bought that countertop.
The cabinet itself I built from scratch -- it cost about half the price of a pre-built one, and I designed it to handle the weight of full carboys. Given the way I over-engineer things, an elephant could stand on it without breaking it, but I'm ok with that. Better too strong than too weak.